Fix menu behavior in phone mode.

This is the same basic fix we made in article.js to correct the handling of expand/collapse sections -- basically, instead of testing the media query once, test in the click event handlers, so we correctly handle devices that switch between wide & narrow modes.

Renato, can you review this? We'll need Ben for the official LGTM.

NOTRY=true

BUG=343400

Review URL: https://codereview.chromium.org/156553007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251856 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251856